1. Field of the Invention:
This invention relates to an easily openable tightly sealed plastic bag so fabricated that it can safely retain the practical strength normally expected of any bag, avoid accidentally sustaining rupture while the bag is being transported or handled, and be opened with the force of finger tips, to a method for the production thereof, and to a tool to be used in working the method.
2. Description of the Prior Art:
Plastic films and laminated films made of superposed layers of plastics, aluminum foil or other metals, paper, and other materials are light in weight, excel in airtightness, and possess high strength and ease of handling. Bags made of such films can be tightly sealed simply by heat-sealing without particularly requiring use of any adhesive agent. Owing to these merits, the films have been recently used extensively to produce tightly sealed bags for various commodities such as foodstuffs, pharmaceutical products, and sundries which come in various forms such as liquid, powder, paste, and solid.
In such a tightly sealed bag as described above, the strong point owned by the material of the bag ironically offers resistance to tearing and renders the bag hardly openable. Generally, the film for use in the tightly sealed bag is tough but, once a cut is inflicted in the bag, is liable to propagate the cut. When one point somewhere in the edge of the bag is cut in advance, therefore, the bag can be opened by the force of finger tips applied so as to widen the cut.
The method of forming an I notch of not less than 2 mm in length in the transverse direction in advance somewhere in the heat-sealed edge of a bag of such a film has been already employed. This method, however, has a disadvantage that the notch so formed in the edge of the bag can not be found readily. The method of forming a V notch somewhere in the edge of a bag of such a film is also used. In accordance with this method, it is somewhat easy to find the notch formed in the bag. When this method is employed where a large number of bags are produced and packed, there is a possibility that V-shaped film scraps resulting from the insertion of V notches will scatter, adhere to the packed products, and deteriorate the factory environment. U.S. Pat. No. 3,650,461 discloses an invention which forms a circular through hole in a sealed portion of a bag. This method also gives rise to a circular scrap and entails a problem similar to the problem suffered by the aforementioned method of inserting a V notch. Moreover, the bag bearing the circular through hole has a problem that desired tearing of the bag necessitates considerably large force because of the force of finger tips applied in an effort to start a tear in the bag results in concentration of stress around the boundary of the circular through hole and consequent elongation of the bag around the circular through hole.
In any of the methods described above, since the point for starting a tear in the bag is formed at a specific location, it does not always turn out to be an advantageous location. There is a possibility that a tear will propagate in an unexpected direction and induce unexpected spilling of the contents. In the case of the method of inserting an I notch or a V notch, since the notch is generally large (at least 2 mm in length), the notch inserted in the film before its fabrication into a bag renders the film readily tearable and even prevents the film from being effectively fabricated into a bag.
Japanese Utility Model Publication No. 22,484/1979 discloses a bag of plastic film having, as points for starting a tear in the bag, a plurality of small punched holes, small embossed holes, or small slits of successively decreasing sizes arranged inwardly from the edge of the bag in at least one of the sealed sides of the bag. Of the bags proposed by this Publication No. 22,484/1979, those provided with small punched holes and small slits have a disadvantage that once tears start in these bags, they rapidly propagage along the rows of holes or slits which are provided to start a tear, and the tears so growing induce fracture of bags to spill their contents while the bags are being transported or handled. The bag provided with embossed holes have a disadvantage that since the holes are merely depressed and are not perforated, they do not easily start tears in the bag unless they are exposed to fairly great force.
Japanese patent application Laid-open No. 160251/1983 discloses a tightly sealed dispensing bag possessing at least three heat-sealed edges and having a multiplicity of scratches closely formed in edge portions of the bag substantially perpendicularly to the edges. The scratches in this bag are formed as by rubbing with a grindstone and the like. This dispensing bag, therefore, has a disadvantage that the scratched surface caused by the rubbing is conspicuous and impairs its external appearance. There is also a possibility that the scratches are liable to be irregular and uneven in size and direction, causing the bag to be opened with difficulty, and the direction of tearing is not uniform.
Besides the various problems described above, the conventional bags have a disadvantage that they are openable only partially depending on how the bags are formed. For example, in the case of the so-called pillow type bag having a notch and a sealed portion formed in the longitudinal direction at the center and the sealed portion produced by overlapping and heat-sealing the opposed ends of the film without allowing the heat-sealed ends to protrude from the boundary of the bag as illustrated in FIG. 20 and FIG. 21, a tear started from the notch 7 ceases to propagate after reaching the heat-sealed portion, leaving the bag only half opened. In this case, it causes inconvenience that the content of the bag has to be drawn out through the small opening barely formed as described above. Where the content is in a solid shape, it is particularly hard to pull out of the bag. It also causes a disadvantage that since the bag is hardly opened it is quite difficult to take out its contents when the width of the contents such as of a medically used articles is very close to that of the bag.